The transmission of the present invention includes a three speed ratio gear system commonly referred to as a Simpson gear set, and a two speed ratio simple planetary gear unit arranged in series. In this respect, the gearing of the transmission of the present invention has features that are common to the gearing arrangement of U.S. Pat. No. 5,586,029, which has four forward driving speed ratios and a single reverse speed ratio. A five speed ratio version of the gearing of the '029 patent is described in U.S. Pat. No. 5,642,283. Reference may be made to these patents to supplement the disclosure of the present invention. They are owned by the assignee of the present invention and are incorporated herein by reference.
The simple planetary gear unit of the '283 patent is used to establish an additional ratio having a numerical value that is greater than the lowest ratio of the four speed gearing of the '029 patent, but which is less than the second ratio of the gearing of the '029 patent. A transition from the second ratio to the third ratio of the present transmission, like the corresponding ratio transition of the transmission of the '283 patent, involves a swapping or interchanging of reaction elements for the simple planetary gear unit and for the Simpson gear unit. The additional ratio converts the four speed gearing of the transmission of the '029 patent into a five speed ratio transmission.
Ratio changes in the five speed ratio version of the transmission may be controlled by a control valve system of the kind disclosed in U.S. Pat. No. 5,646,842. This involves the use of a reaction brake and a drive clutch, where the reaction brake establishes a reaction point for the common sun gear of the Simpson gear set and the drive clutch establishes a gear ratio of unity for the Simpson planetary gear set. The transition between second and third gear ratio involves the simultaneous engagement of the drive clutch and the disengagement of the reaction brake, which is referred to as a synchronous reaction-to-drive shift. The 3-2 downshift is the reverse of a 2-3 shift and is referred to as a synchronous drive-to-reaction shift.
A non-synchronous adaptation of a gearing arrangement of the kind shown in the preceding patents would include an overrunning coupling and a friction brake for establishing a reaction point for the common sun gear of the Simpson gear set and a separate overrunning coupling for clutching together two elements of the simple planetary gear unit. An upshift from the third ratio to the fourth ratio and a downshift from the fourth ratio to the third ratio, as well as a downshift from the fifth ratio to the third ratio in the non-synchronous version of the gearing, require the use of two overrunning couplings and the engagement or release of only a single friction element. The control of these ratio shifts requires the engagement and release of the reaction brake or clutch on upshifts and downshifts.
To control the friction elements of the transmission of the '842 patent, a single variable force solenoid is used to establish the reaction brake pressure for the Simpson gear set reaction point as well as the reaction brake pressure for the simple planetary gear unit. A friction clutch, which is used to establish a third speed ratio, has its pressure controlled by the same variable force solenoid. The clutch that is used for third (fourth in 5-speed version) speed ratio operation is the same clutch that is used for reverse operation. Thus the capacity of the clutch must be established at a high level. Because of the driveline torque requirements for reverse, that torque level is greater than the torque level that is needed for establishing a reaction point for third (fourth in 5-speed version) speed ratio operation. The absence of independent control of the high ratio clutch and the reaction brake for third ratio operation leads to a design compromise that might affect shift quality of the transmission during upshifts from the third ratio to the fourth ratio, as well as downshifts from the fourth ratio to the third ratio and from the fifth ratio to the third ratio.